1. Field of the Invention
The present invention relates to film cartridges and films which have digital code patterns representing information of the films and to cameras which are adapted for use with such film cartridges or films.
2. Description of the Prior Arts
Various film cartridges and films of the above described type and cameras adapted for use therewith are known by, for example, U.S. Pat. Nos. 4,024,557 and 4,200,371 and RESEARCH DISCLOSURE April 1980 Number 192 particularly on page 142.
The prior art film cartridges, films and cameras are advantageous in that it is made possible to automatically read out and set the information on the film cartridges or on the films. However, there are the following problems which are left unsolved.
(a) With prior art cameras in which sensing or detecting contacts are fixedly provided in a cartridge chamber, insertion of a film cartridge into the chamber is possible disturbed by the contacts. With other type prior art cameras in which sensing or detecting contacts project into a cartridge chamber in association with closure of a camera back cover against a spring bias, the back cover must be opened again troubling the camera user where a film cartridge containing a film whose film speed is not consistent with that intended by the camera user is inserted into the chamber causing the camera to indicate such unintended film speed.
(b) With prior art film cartridges having a digital code pattern representing film information such as film speed, the code pattern is designed only by numbering film speeds low to high by using binary codes, so that outputs from a reading device must be decoded in cameras.
(c) With prior art films having a digital code pattern with perforated and non-perforated areas at its leader portion and with prior art cameras which read the patterns at an exposure station, a memory device is required which memorizes outputs from a reading device even after the leading portion of the film has passed the exposure station. Additionally, where the reading device is provided on a camera back cover or on a film pressure plate electric connection between the reading device and circuits within a camera body becomes troublesome.
(d) Film speeds are divided by 1/3 EV steps according to the APEX system while it is usual for digital calculations to put weights of 1/2, 1/4 and 1/8 on decimal or fractional bits. Thus, decimal APEX values of film speeds are not suited for digital calculations to be effected in camera circuits such as an exposure control circuit.
(e) Furthermore, it is not always necessary but rather useless for armature cameras to set film speeds by 1/3 EV steps since such armature cameras are usually designed to control an exposure with a few predetermined steps allowing occurrence of little errors.
(f) With prior art film cartridges having digital code patterns shown in FIG. 2, all bits of the code patterns representing film speeds have different weights. More particularly, the patterns include a first bit conductive for all film speeds and second to sixth bits conductive and nonconductive in dependence upon the film speeds and the second to sixth bits have weights of 4, 2, 1, 2/3 and 1/3 respectively. However, the code pattern representing ASA or ISO 25 is designed such that only the first bit is conductive. This makes it necessary to provide two contacts for detecting the condition of the first bit and therefore the film cartridge having the code pattern of ASA or ISO 25 cannot be discriminated from an ordinary film cartridge having no such code patterns in case space inside a camera body does not allow to arrange two contacts for the first bit.